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<div class="section">
<div class="titlepage"><div><div>
<h2 class="title">
<a id="_finding_multiple_exact_values"></a>查找多个精确值<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/080_Structured_Search/15_terms.asciidoc">edit</a>
</h2>
</div></div></div>
<p><code class="literal">term</code> 查询对于查找单个值非常有用，但通常我们可能想搜索多个值。  如果我们想要查找价格字段值为 $20 或 $30 的文档该如何处理呢？</p>
<p>不需要使用多个 <code class="literal">term</code> 查询，我们只要用单个 <code class="literal">terms</code> 查询（注意末尾的 <em>s</em> ）， <code class="literal">terms</code> 查询好比是 <code class="literal">term</code> 查询的复数形式（以英语名词的单复数做比）。</p>
<p>它几乎与 <code class="literal">term</code> 的使用方式一模一样，与指定单个价格不同，我们只要将 <code class="literal">term</code> 字段的值改为数组即可：</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">{
    "terms" : {
        "price" : [20, 30]
    }
}</pre>
</div>
<p>与 <code class="literal">term</code> 查询一样，也需要将其置入 <code class="literal">filter</code> 语句的常量评分查询中使用：</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /my_store/products/_search
{
    "query" : {
        "constant_score" : {
            "filter" : {
                "terms" : { <a id="CO49-1"></a><i class="conum" data-value="1"></i>
                    "price" : [20, 30]
                }
            }
        }
    }
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/080_Structured_Search/15_Terms_filter.json"></div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO49-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>这个 <code class="literal">terms</code> 查询被置于 <code class="literal">constant_score</code> 查询中</p>
</td>
</tr>
</table>
</div>
<p>运行结果返回第二、第三和第四个文档：</p>
<div class="pre_wrapper lang-json">
<pre class="programlisting prettyprint lang-json">"hits" : [
    {
        "_id" :    "2",
        "_score" : 1.0,
        "_source" : {
          "price" :     20,
          "productID" : "KDKE-B-9947-#kL5"
        }
    },
    {
        "_id" :    "3",
        "_score" : 1.0,
        "_source" : {
          "price" :     30,
          "productID" : "JODL-X-1937-#pV7"
        }
    },
    {
        "_id":     "4",
        "_score":  1.0,
        "_source": {
           "price":     30,
           "productID": "QQPX-R-3956-#aD8"
        }
     }
]</pre>
</div>
<div class="section">
<div class="titlepage"><div><div>
<h3 class="title">
<a id="_包含而不是相等"></a>包含，而不是相等<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/080_Structured_Search/20_contains.asciidoc">edit</a>
</h3>
</div></div></div>
<p>一定要了解 <code class="literal">term</code> 和 <code class="literal">terms</code> 是 <em>包含（contains）</em> 操作，而非 <em>等值（equals）</em> （判断）。  如何理解这句话呢？</p>
<p>如果我们有一个 term（词项）过滤器 <code class="literal">{ "term" : { "tags" : "search" } }</code> ，它会与以下两个文档 <em>同时</em> 匹配：</p>
<div class="pre_wrapper lang-js">
<pre class="programlisting prettyprint lang-js">{ "tags" : ["search"] }
{ "tags" : ["search", "open_source"] } <a id="CO50-1"></a><i class="conum" data-value="1"></i></pre>
</div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO50-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>尽管第二个文档包含除 <code class="literal">search</code> 以外的其他词，它还是被匹配并作为结果返回。</p>
</td>
</tr>
</table>
</div>
<p>回忆一下 <code class="literal">term</code> 查询是如何工作的？ Elasticsearch 会在倒排索引中查找包括某 term 的所有文档，然后构造一个 bitset 。在我们的例子中，倒排索引表如下：</p>
<div class="informaltable">
<table border="1" cellpadding="4px" width="50%">
<colgroup>
<col class="col_1">
<col class="col_2">
</colgroup>
<tbody>
<tr>
<td align="left" valign="top"><p>Token</p></td>
<td align="left" valign="top"><p>DocIDs</p></td>
</tr>
<tr>
<td align="left" valign="top"><p><code class="literal">open_source</code></p></td>
<td align="left" valign="top"><p><code class="literal">2</code></p></td>
</tr>
<tr>
<td align="left" valign="top"><p><code class="literal">search</code></p></td>
<td align="left" valign="top"><p><code class="literal">1</code>,<code class="literal">2</code></p></td>
</tr>
</tbody>
</table>
</div>
<p>当 <code class="literal">term</code> 查询匹配标记 <code class="literal">search</code> 时，它直接在倒排索引中找到记录并获取相关的文档 ID，如倒排索引所示，这里文档 1 和文档 2 均包含该标记，所以两个文档会同时作为结果返回。</p>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>由于倒排索引表自身的特性，整个字段是否相等会难以计算，如果确定某个特定文档是否 <em>只（only）</em> 包含我们想要查找的词呢？首先我们需要在倒排索引中找到相关的记录并获取文档 ID，然后再扫描 <em>倒排索引中的每行记录</em> ，查看它们是否包含其他的 terms 。</p>
<p>可以想象，这样不仅低效，而且代价高昂。正因如此， <code class="literal">term</code> 和 <code class="literal">terms</code> 是 <em>必须包含（must contain）</em> 操作，而不是 <em>必须精确相等（must equal exactly）</em> 。</p>
</div>
</div>
</div>

<div class="section">
<div class="titlepage"><div><div>
<h3 class="title">
<a id="_精确相等"></a>精确相等<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/080_Structured_Search/20_contains.asciidoc">edit</a>
</h3>
</div></div></div>
<p>如果一定期望得到我们前面说的那种行为（即整个字段完全相等），最好的方式是增加并索引另一个字段， 这个字段用以存储该字段包含词项的数量，同样以上面提到的两个文档为例，现在我们包括了一个维护标签数的新字段：</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">{ "tags" : ["search"], "tag_count" : 1 }
{ "tags" : ["search", "open_source"], "tag_count" : 2 }</pre>
</div>
<div class="sense_widget" data-snippet="snippets/080_Structured_Search/20_Exact.json"></div>
<p>一旦增加这个用来索引项 term 数目信息的字段，我们就可以构造一个 <code class="literal">constant_score</code> 查询，来确保结果中的文档所包含的词项数量与要求是一致的：</p>
<div class="pre_wrapper lang-sense">
<pre class="programlisting prettyprint lang-sense">GET /my_index/my_type/_search
{
    "query": {
        "constant_score" : {
            "filter" : {
                 "bool" : {
                    "must" : [
                        { "term" : { "tags" : "search" } }, <a id="CO51-1"></a><i class="conum" data-value="1"></i>
                        { "term" : { "tag_count" : 1 } } <a id="CO51-2"></a><i class="conum" data-value="2"></i>
                    ]
                }
            }
        }
    }
}</pre>
</div>
<div class="sense_widget" data-snippet="snippets/080_Structured_Search/20_Exact.json"></div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO51-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>查找所有包含 term <code class="literal">search</code> 的文档。</p>
</td>
</tr>
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO51-2"><i class="conum" data-value="2"></i></a></p>
</td>
<td align="left" valign="top">
<p>确保文档只有一个标签。</p>
</td>
</tr>
</table>
</div>
<p>这个查询现在只会匹配具有单个标签 <code class="literal">search</code> 的文档，而不是任意一个包含 <code class="literal">search</code> 的文档。</p>
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